This invention relates to continuous mixers and/or processors having at least two side by side parallel mixer shafts extending through an elongate barrel having walls of the configuration of a plurality of intersecting cylinders, and having radially interacting, self-wiping, and also barrel-wiping, mixing and conveying members on each shaft. In such machinery which may be used for mixing, blending, compounding, reacting, devolatilizing, pyrolytically combusting, and the like, a material entrance is provided at one end of the barrel and a material discharge is provided at the other.
Multiple shaft mixers of this type are well suited to the power mixing and kneading of a continuous flow of synthetic plastic and like materials and subject the material being processed to intense shearing and kneading forces. In mixing machines of this type, interwiping mixing paddles or worms are fixed on the elongate shafts which are driven at the same speed in the same direction of rotation. Materials of the type processed in such mixers now, or to be processed in the future, require the application of ever higher forces to efficiently process the material at the higher rates of production desired, but the application of sufficiently high forces to the material in present day machinery is complicated by a number of factors. After the geometry of a twin shaft, co-rotating mixer is determined, a fixed shaft to shaft center distance to bore diameter ratio must be maintained in order for the radially opposite mixing paddles to co-wipe, and, at the same time, completely wipe the interior of the mixing chamber. Shaft deflection is a major potential source of difficulty and the shafts must be sufficiently heavy duty so that deflection is limited. This dictates the relatively close spacing of large diameter shafts which limits the size of the gear teeth that can be used to drive the shafts. It is further necessary that the machine be kept relatively compact, and of not undue length, and that there be an equal torque distribution to each of the two mixing shafts. Typical machines of this general character are disclosed in the present assignees prior U.S. Pat. Nos. 3,195,868; 3,198,491; 3,423,074; 3,463,459; 3,387,826; and 3,779,522, which are incorporated herein by reference. As a matter of background, other patents which are known to applicant are as follows:
______________________________________ 819,800 Richards 1,371,046 Mosher 1,587,300 Hanley, Jr. 3,749,374 Buchheit 3,901,482 Kieffaber 3,907,259 Leclercq ______________________________________
The E. L. Richards U.S. Pat. No. 819,800, discloses a machine in which the shafts are driven from opposite ends. Patents which disclose single motor drives are disclosed in Hanley U.S. Pat. No. 1,587,300 and Mosher U.S. Pat. No. 1,371,046. The Buchheit U.S. Pat. No. 3,749,374 discloses a dual drive arrangement in which separate drive motors drive each of the screws. None of the patents singularly or combinatively are considered to be materially pertinent to the invention claimed.